Anyone else find their garden office gets unbearably hot in summer even with decent insulation?

Mine's a motorhome rather than a garden office, but the physics is basically the same — insulation keeps heat in as brilliantly as it keeps it out, which is lovely news in February and absolutely diabolical in July.

Couple of things that've genuinely helped me:

• Reflective foil on south-facing windows — sounds naff, looks naff, works brilliantly
• A small 12V fan running continuously to shift air rather than just baking in a static pocket of misery
• Ventilation positioning matters more than insulation thickness — top vents letting hot air escape upward changed everything for me

The real villain nobody talks about is thermal mass. A well-insulated box with no mass heats up fast and stays hot. Brick garden offices cope better because the bricks absorb heat slowly. Timber frames with insulation batts are essentially a thermos flask pointed at the sun.

I've seen people chuck expensive portable AC units at the problem and just end up with an expensive hot room because the exhaust hose situation is a disaster.

What's your setup — timber frame, insulated panels, something else? And are you running any active ventilation or purely passive? Genuinely curious whether a proper heat recovery ventilation unit would be overkill for a garden office or if it'd actually pay for itself in comfort terms.

Someone on here must have cracked this — or are we all just collectively suffering from June through August? 😅

@AlexHobbs this is exactly my problem with my static caravan — even with the upgraded insulation I had put in, July and August are brutal. The walls basically become a heat store by mid-afternoon.

What's helped me most is a 12v compressor cooler running off my Victron setup, combined with reflective foil across the south-facing windows. Not proper air con but it takes the edge off.

Has anyone actually fitted a proper mini-split air conditioning unit to a static or similar structure? I've seen some that can run reasonably efficiently on solar but I'm genuinely unsure whether my battery bank is realistically sized to cope overnight. What sort of watt-hours are people finding these things draw in practice?

@AlexHobbs the cruel irony of insulation — you spend good money making your space into a thermos flask and then act surprised when it works both ways 😅

My garden office hits about 38°C by 2pm on a decent July day despite 100mm PIR throughout. The solar panels on the roof do at least power a decent

Phase change materials in the walls are worth a look — basically fancy wax that absorbs heat as it melts during the day and releases it at night, sounds bonkers but my garden office stays noticeably cooler since I lined the ceiling with the stuff.

@NorfolkVanLifer the phase change material route is genuinely fascinating — been down that rabbit hole myself.

What actually made the biggest difference in my van though was reflective window film on the south-facing glass. Spent a weekend last August sweating through the job, convinced it was pointless, then sat inside the following Monday absolutely gobsmacked. Thermal mass is brilliant but in a small space you need to stop the solar gain arriving in the first place rather than just absorbing it once it's through.

Combined that with a small 12V fan running off the Victron system to create cross-ventilation through the roof vent — keeps air moving without hammering the battery. The insulation does its job properly once the sun dips; it's just that midday window you need to fight differently.